The tread patterns of pneumatic radial tires are often determined mainly in view of the desired performance of the tire, such as maneuvering stability and wet performance. Also, it is conventional practice that the tread is formed with a plurality of grooves extending in the circumferential direction and widthwise direction of the tire, to thereby define discrete land portions in the form of blocks. In this instance, there is a tendency that the tread undergoes irregular wear. One may then consider that the block configuration can be modified for the purpose of preventing irregular wear of the tread, though such modifications are not practically carried out. This is because modification of the block configuration makes it difficult to preserve the maneuvering stability, wet performance and the like, which are required as the basic performance of the tire. Accordingly, it would be desirable to suppress irregular wear of the tread by improving the belt structure.